Royal Murders, Scandals, and Secrets: Mad King Eric

In history, there have been several monarchs known as “Mad Kings” - monarchs who were plagued by erratic and even violent behavior often attributed to mental illness. King Eric the XIV of Sweden is one such ruler. While intellectually brilliant, King Eric suffered from extreme paranoia, which led to erratic, violent, and even murderous behavior.

Sources: 
Disturbed Facts About Eric XIV Of Sweden, The Butcher King - Factinate
Eric XIV, King of Sweden, Britannica.com 
https://www.britannica.com/biography/Erik-XIV

Karin Mansdotter, wikipedia.com 
https://en.wikipedia.org/wiki/Karin_Månsdotter